The present invention relates to a magnetic disk apparatus and, more particularly, to a magnetic disk apparatus comprising an air bearing head slider which flies over a surface of a rotating magnetic disk using a contact-start-stop technique wherein the head slider contacts the magnetic disk surface when the magnetic disk stops.
A magnetic disk apparatus of this kind comprises a spindle motor for rotating the magnetic disk and a head slider provided with an electromagnetic transducer thereon. The head slider is supported by a flexible suspension member to face the magnetic disk surface. The suspension member is fastened to a head arm driven by a head position actuator. Due to the air pressure caused by the rotation of the magnetic disk, the head slider flies at a constant spacing from the magnetic disk. Under this condition, the position actuator moves the head slider in a radial direction of the magnetic disk to position the transducer at the object track on the magnetic disk.
In response to the stoppage of the magnetic disk, the head slider contacts the surface of the magnetic disk by means of the resilient force of the suspension member. As is described in U.S. Pat. No. 4,194,226, in order to avoid contacting the head slider with the data zone on the surface of the magnetic disk, there is provided a contact-start-stop zone (hereunder referred to as "CSS zone") or landing zone at the innermost or outermost circumference of the disk. When the magnetic disk apparatus is not operated, that is, the disk does not rotate, the head slider is disposed at a position in the CSS zone and contacts the magnetic disk. Upon start-up of the magnetic disk apparatus, the head slider is retained at a position in the CSS zone until the rotation of the magnetic disk reaches a constant speed. Therefore, the head slider slides upon the CSS zone on the surface of the magnetic disk, until it becomes airborne. At the termination of the disk operation, the rotation of the magnetic disk is stopped after the head slider is again positioned in the CSS zone. Therefore, as the rotational speed of the disk decreases, the head slider gradually approaches the CSS zone of the disk surface and finally slides on the CSS zone. When the disk stops completely, the head slider contacts a portion of the CSS zone. Thus, the CSS zone is used as a runway for the head slider.
The conventional magnetic disk apparatus is constructed so that the head slider is positioned at the same location (same track) within the CSS zone during the rotation start and stop periods of the magnetic disk. Therefore, the frictional force applied by the suspension member is applied to the same portion of the surface of the CSS zone for each start/stop of the disk. The abrasion of the head slider against the magnetic disk due to the sliding contact shortens the life of the magnetic disk apparatus. Since the material of the head slider is usually harder than that of the magnetic disk, the abrasion of the magnetic disk is more important. If it is assumed that the amount of abrasion of the disk in the CSS zone per unit length is V.sub.w, the circumferential length of the CSS zone is l.sub.c, the number of revolutions required to achieve complete flying of the head slider is N.sub.t, and the length of the head slider is L.sub.s, the following relation is approximately established among the above quantities. EQU V.sub.w .varies.N.sub.t L.sub.s /l.sub.c ( 1)
From equation (1), it is obvious that V.sub.w becomes greater as l.sub.c decreases. In other words, magnetic disks of smaller radius, such as 5.25 and 3.5 inches, suffer from considerable abrasion. In order to overcome this problem, either N.sub.t or L.sub.s, or both must be chosen to be small. However, this has been found to be impossible for the following reasons. First, in order to make N.sub.t small, it is necessary to use a spindle motor whose rotation rapidly reaches the constant speed. This inevitably causes the size of the spindle motor to be large, so that it is not suitable for a magnetic disk apparatus of small disk size. Next, the selection of small L.sub.s is limited due to the size and shape of the magnetic head slider, which are determined by electromagnetic requirements and by the requirement to obtain the necessary flying height.
Since dust produced due to the abrasion of the magnetic disk may find its way into the gap between the head slider and the disk during read/write operation, it is possible that the suspension member of the head slider and the surface of the disk may be irreparably damaged. This phenomenon is known as "head crash".